Yesterday, after half a month of speculation, Microsoft announced that it purchased Yammer for $1.2 billion. According to Charles River Partners, the first venture capital firm to invest in Yammer, that’s the second largest all-cash deal for a VC-backed company, ever. VentureBeat has been reaching out to industry sources — and the original Yammer investor, George Zachary — asking what this deal means for the enterprise social market. Here’s what we’re hearing.